[clang] [modules] Accept equivalent module caches from different symlink (PR #90925)

[Ellis Hoag via cfe-commits]

https://github.com/ellishg updated https://github.com/llvm/llvm-project/pull/90925

>From 4760ebce0ff7725f4bb75f5107f551d867e4db6d Mon Sep 17 00:00:00 2001
From: Ellis Hoag <ellis.sparky.hoag at gmail.com>
Date: Thu, 2 May 2024 17:47:38 -0700
Subject: [PATCH 1/2] [modules] Accept equivalent module caches from different
 symlink

Use `fs::equivalent()`, which follows symlinks, to check if two module cache paths are equivalent. This prevents a PCH error when building from a different path that is a symlink of the original.

```
error: PCH was compiled with module cache path '/home/foo/blah/ModuleCache/2IBP1TNT8OR8D', but the path is currently '/data/users/foo/blah/ModuleCache/2IBP1TNT8OR8D'
1 error generated.
```
---
 clang/lib/Serialization/ASTReader.cpp | 20 +++++++++-----------
 clang/test/Modules/module-symlink.m   | 11 +++++++++++
 2 files changed, 20 insertions(+), 11 deletions(-)
 create mode 100644 clang/test/Modules/module-symlink.m

diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 0ef57a3ea804ef..c20ead8b865692 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -839,17 +839,15 @@ static bool checkHeaderSearchOptions(const HeaderSearchOptions &HSOpts,
                                      DiagnosticsEngine *Diags,
                                      const LangOptions &LangOpts,
                                      const PreprocessorOptions &PPOpts) {
-  if (LangOpts.Modules) {
-    if (SpecificModuleCachePath != ExistingModuleCachePath &&
-        !PPOpts.AllowPCHWithDifferentModulesCachePath) {
-      if (Diags)
-        Diags->Report(diag::err_pch_modulecache_mismatch)
-          << SpecificModuleCachePath << ExistingModuleCachePath;
-      return true;
-    }
-  }
-
-  return false;
+  if (!LangOpts.Modules || PPOpts.AllowPCHWithDifferentModulesCachePath ||
+      SpecificModuleCachePath == ExistingModuleCachePath ||
+      llvm::sys::fs::equivalent(SpecificModuleCachePath,
+                                ExistingModuleCachePath))
+    return false;
+  if (Diags)
+    Diags->Report(diag::err_pch_modulecache_mismatch)
+        << SpecificModuleCachePath << ExistingModuleCachePath;
+  return true;
 }
 
 bool PCHValidator::ReadHeaderSearchOptions(const HeaderSearchOptions &HSOpts,
diff --git a/clang/test/Modules/module-symlink.m b/clang/test/Modules/module-symlink.m
new file mode 100644
index 00000000000000..be447449a0e81e
--- /dev/null
+++ b/clang/test/Modules/module-symlink.m
@@ -0,0 +1,11 @@
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -fmodules-cache-path=%t/modules -fmodules -fimplicit-module-maps -I %S/Inputs -emit-pch -o %t.pch %s -verify
+
+// RUN: ln -s %t/modules %t/modules.symlink
+// RUN: %clang_cc1 -fmodules-cache-path=%t/modules.symlink -fmodules -fimplicit-module-maps -I %S/Inputs -include-pch %t.pch %s -verify
+
+// expected-no-diagnostics
+
+ at import ignored_macros;
+
+struct Point p;

>From 490eefe98e3dd020ff3e51c7f817ec2b3d3a2663 Mon Sep 17 00:00:00 2001
From: Ellis Hoag <ellis.sparky.hoag at gmail.com>
Date: Fri, 3 May 2024 09:50:11 -0700
Subject: [PATCH 2/2] Require shell to fix windows test

---
 clang/test/Modules/module-symlink.m | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/clang/test/Modules/module-symlink.m b/clang/test/Modules/module-symlink.m
index be447449a0e81e..9a69186c5ea28f 100644
--- a/clang/test/Modules/module-symlink.m
+++ b/clang/test/Modules/module-symlink.m
@@ -1,3 +1,5 @@
+// REQUIRES: shell
+
 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fmodules-cache-path=%t/modules -fmodules -fimplicit-module-maps -I %S/Inputs -emit-pch -o %t.pch %s -verify